1. Field of the Invention
This invention relates to an improved method of and apparatus for determining the weight of web material fed to a processing station.
2. Description of Related Art
It is known, in a number of manufacturing processes, to use a basis weight scanner to monitor for variations in thickness of sheet material passing a monitoring point in a manufacturing process. One known form of basis weight scanner utilises a beta-particle emitter on one side of the moving sheet material and a beta-particle detector on the other side of the moving sheet material, the emitter and detector being moved together as a pair across a substantial part of the width of the sheet material to monitor variations in thickness of the sheet material by a sensing of real time variations in beta-particle absorption by the sheet material.
Such a basis weight scanner is used, for example, to monitor the output of a sheet extruder in a plastics processing plant downstream of an extruding head and, via a feedback loop, to adjust the performance of the extruding head to maintain substantially uniform product thickness across the width of the sheet material.
U.S. Pat. No. 4,854,730 discloses equipment for determining the content of fillers in paper which equipment uses a beta-ray source to evaluate the basis weight of the cellulose in the paper but the equipment described is not used to scan across the entire width of a web of paper to determine the total weight of cellulose as is practised by the present invention.
We have now found that a basis weight scanner can be used as a flow meter to determine the total weight of sheet material fed forward to a subsequent processing plant.